The present invention generally relates to electrical energy management systems. More particularly, the invention relates to energy accumulation systems for use in conjunction with generative power sources.
Due to developments in power electronics and an increase in the requirements for emergency and stored energy, higher voltages and power levels are required from batteries. Various electrical functions in aerospace and ground vehicles (tactical vehicles and automotive) may be performed with power systems which incorporate energy storage elements such as batteries supercapacitors and/or fuel cells. These applications may include aircraft APU and main engine start and ground vehicle traction drives. Energy accumulators may be employed for effective harnessing or mitigation of bidirectional flow of electric energy and improving overall efficiency.
Some large scale energy storage systems may also be employed to satisfy mobile power and distributed renewable applications for peak power shaving and/or effectively using stored energy to avoid high cost of electricity during higher rates imposed by smart metering. In many of these applications, elementary battery cells may be connected in series so that an output terminal voltage equals a sum of elementary voltages.
In addition, many newer systems may employ Li-ion batteries which consist of multiple cells in series. The number of cells in series increase with the increased battery voltage. Conventional Li-ion systems require charge/discharge control and equalization at the cell level which may require considerable electronics, particularly in case of the higher voltage batteries.
In such systems it is important to provide reliable output from the batteries. For example it is important to assure that degradation of any one cell (e.g. excessive capacity fading, voltage imbalance, open cell) does not lead to the failure of an entire system. In systems which require a large number of cells connected in series, the overall reliability of the system must be carefully managed.
As can be seen, there is a need for a power management system with an energy accumulator that has high reliability and is not subject to failure as a result of failure on any one particular cell in a battery pack. Additionally there is a need to lower the number of the cells used in higher voltage systems through use of boost converters.